Methamphetamines produce a feeling of intense euphoria by boosting levels of the neurotransmitter dopamine in the brain.

Because Parkinson’s disease symptoms appear when dopamine producing cells stop functioning normally, scientists had long suspected a link with meth use but had been unable to prove it because Parkinson’s typically develops in middle and old age. Methamphetamine addiction is a relatively recent phenomenon.

Researchers from the Centre for Addiction and Mental Health in Canada studied almost 300,000 hospital records covering 16 years from California, a state with a high rate of methamphetamine use.

Between 1990 and 2005, at least 40,472 people were hospitalised for amphetamine use disorder.

That group was compared with 35,335 people diagnosed with cocaine use disorders because cocaine also affects dopamine. The researchers wanted to see if the link was caused by methamphetamines specifically.

A control group of 207,831 people hospitalised for appendicitis with no addiction was also included in the study.

“We found that meth/amphetamine users had a 76% increased risk of developing Parkinson’s disease in comparison to a matched population-proxy control group,” the researchers wrote in a paper published in the journal Drug and Alcohol Dependence.

The authors said this means if 10,000 people with methamphetamine dependence were followed over 10 years, 21 would develop Parkinson’s, compared with 12 people out of 10,000 from the general population.

“The cocaine group did not show elevated hazard of Parkinson’s disease compared to the matched appendicitis group,” the paper said.

The researchers said the findings do not apply for people who take amphetamines for medical conditions such as attention deficit hyperactivity disorder (ADHD) because the dosages in medicated amphetamine use are much lower.

“Given that methamphetamine and other amphetamine stimulants are the second most widely used illicit drugs in the world, the current study will help us anticipate the full long-term medical consequences of such problematic drug use,” said lead researcher, Dr Russell Callaghan.